An update on the development of an accelerated aging method for roofing materials

Transcription

1 An update on the development of an accelerated aging method for roofing materials MohamadSleiman, Thomas W. Kirchstetter, Haley E. Gilbert, Paul H. Berdahl, Hugo Destaillats, Ronnen Levinson Lawrence Berkeley National Laboratory, Berkeley, CA and Hashem Akbari Concordia University, Montreal, Canada. 1 Building Technologies Program Asphalt Roofing Manufacturers Association Spring Committee Meeting, Denver, CO April 16, 2013

2 Benefits of cool roofs Replacing a dark roof with a cool roof can help Reduce annual cooling energy use by 5-20% (Levinson et al. 2005) Mitigate the heat island effect (Rosenfeld et al. 1998; Akbari et al. 2001) Delay global warming (10 tonnesof CO 2 offset by 100 m 2 white roofing) (Menonet al. 2010; Akbariet al. 2009; Oleson et al. 2010) 2

3 Making U.S. commercial building roofs white would offer $11B in lifetime energy savings Retrofitting 80% of U.S. air-conditioned commercial buildings with conventional white roofs would annually save $735M New York Times, 30 July Mt CO 2 (=1.2M cars) through energy conservation Levinson R, Akbari H Energy Efficiency 3:53-109

4 Berkeley Lab s Heat Island Group works to cool buildings, cities and the planet Improve the performance of cool roofing materials rating (CRRC), standards (ASTM, ISO) accelerated aging methods next gen materials (cool colored pigments, retention of high SR) Engage stakeholders smart choices about cool surfaces government, NGOs Advance the science of heat island mitigation mapping urban albedosusing aerial imagery satellite measurements of radiative heat flows International collaborations dissemination of cool roofing technologies worldwide 4

5 Aging = soiling + weathering wet deposition: soot, salts, organics 2010 dry deposition: mineral dust 2012 microbiological growth: fungi, mold, bacteria Challenge: speed the development of high performance building envelope materials that resist soiling, maintain high solar reflectance, and save energy 5

6 Aging markedly decreases solar reflectance of conventional roofs. Aged solar reflectance OHIO (n=586) OHIO (n = 573) CA Title 24 no change Initial solar reflectance running mean fieldapplied coating clay tile metal roofing single-ply membrane factoryapplied coating concrete tile asphalt shingle modified bitumen Sleimanet al. (2011) Solar Energy Materials and Solar Cells, 95, When a white roof s reflectance falls to 0.60 from 0.80, annual energy savings decrease by ⅓ 6

7 We observe significant differences between the three CRRC sites Aged solar reflectance FLORIDA (n=586) no change running mean CA Title 24 Aged solar reflectance ARIZONA (n=586) no change CA Title 24 running mean Initial solar reflectance Initial solar reflectance Florida Mean absolute loss in solar reflectance Arizona Ohio Initial solar reflectance

8 and significant differences among product categories Aged solar reflectance Factory-applied coating no change running mean CA Title 24 FLORIDA Initial solar reflectance Aged solar reflectance Metal no change CA Title running mean FLORIDA Initial solar reflectance Aged solar reflectance Single-ply membrane CA Title 24 no change running mean FLORIDA Initial solar reflectance 8 Aged solar reflectance Field-applied coating running mean CA Title 24 no change FLORIDA Initial solar reflectance Aged solar reflectance Modified bitumen CA Title 24 no change FLORIDA running mean Initial solar reflectance Aged solar reflectance Tile no change running mean CA Title 24 FLORIDA Initial solar reflectance

9 Factory-applied coating -10 Fractional difference in aged solar reflectance (%) Field-applied coating Metal Modified bitumen Shingle Single-ply membrane Tile 9 Fluctuations in aged solar reflectance with respect to CRRC 3-site average are moderate (R k R CRRC ) R CRRC Sleimanet al. Solar Energy Materials and Solar Cells. 2011;95:3385 Number of samples Florida Arizona Ohio

10 Development of accelerated aging method: Purpose, objectives and approach Problem Statement: CRRC and Energy Star rating programs require three years of natural exposure, delaying introduction of novel cool roofing materials. R&D challenge: Develop technology to quickly rate roofing products, removing barrier to innovation of energy saving roofing materials. Impact: Benefits to society and roofing industry by speeding prototyping and introduction to market of high performance products. Focus: Develop and transfer technology that promotes advanced cool roofs. Wide adoption of cool roofs is projected to yield annual net primary energy savings of nearly 300 TBTU, worth about $2B/year, reduce CO 2 emissions, and partially mitigate global warming. Approach: (1) establish a network of industrial partners, (2) field exposure of 27 products, (3) develop lab method, (4) validate method with inter-laboratory study, (5) develop ASTM and ISO standards for accelerated aging, (6) integrate soiling in a commercial weatherometer to facilitate technology adoption.

11 Roofing products used in this study We screened 100 roofing materials from 40 industrial partners Selected 28 materials from the following categories: fieldapplied coating clay tile single-ply membrane asphalt shingle factoryapplied coating concrete tile metal roofing modified bitumen Selection criteria: diversity of products & colors, market presence, sample uniformity and availability of aged samples. Used for laboratory (accelerated) and natural exposure 11

12 Coupons of 27 products naturally exposed at the three CRRC sites are collected & characterized quarterly temperate (Cleveland, OH) 45 tilt hot & dry (Phoenix, AZ) hot & humid (Miami, FL) JANUARY APRIL JULY OCTOBER 5 tilt 12

13 We measure radiative properties using ASTM standards E903, C1371 & C1549 E 903 Solar Absorptance, Reflectance, and Transmittance of Materials Using Spectrometer w/ Integrated Spheres 13 C 1371 Determination of Emittanceof Materials Near Room Temperature Using Portable Emissometers C 1549 Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer

14 We measure chemical and physical properties of a subset of samples SEM (morphology) 2000 Chemical composition of soiling Laser desorption photoionization TOF-mass spectrometry (ALS) Florida Soot Salts 1500 Ohio Counts Water contact angle (hydrophilicity) m/z 14

15 Some products reach CRRC s 3-year-aged solar reflectance after 1 year of natural exposure; others take longer Solar Reflectance, B891 Method Sample 1: White Single-Ply Membrane, 5 Degree Tilt White single-ply membrane, 5 degree tilt LBNL, Arizona LBNL, Florida LBNL, Ohio CRRC, Arizona CRRC, Florida CRRC, Ohio Number of Months Exposed Since October 2010 Solar Reflectance, B891 Method Sample 2: White Single-Ply Membrane, 5 Degree Tilt LBNL, Arizona LBNL, Florida LBNL, Ohio CRRC, Arizona CRRC, Florida CRRC, Ohio Number of Months Exposed Since October 2010 Natural exposure: Seasonal variability Geographical (climate) variability Precision of aged solar reflectance measurements Validation of accelerated aging method using the same materials 15

16 Accelerated aging: goals and challenges GOALS Develop a reliable lab method for accelerated aging that can be readily adopted by industry Incorporate this method in standards to facilitate worldwide adoption of cool roofs CHALLENGES Method should be tunable to mimic accurately aging of roofing materials in different climate zones Method should reduce complex and variable environmental signatures to a minimum set of parameters 16

17 Chemical composition of soiling on building envelopes Dust 28 66% Salts 23% Salts 18 27% Dust 53% Soot 6% POM 18% Soot 4 12% Particulate Organic Matter 8 36 % soot core salts and organic coating Favezet al, Atmos. Environ, How to mimic natural soiling in the lab?

18 Soiling surrogates used in our laboratory method Salts Clays + Ironoxide Humic acid Soot hydrosol Ozone 18 Methane diffusion flame

19 Soiling apparatus and laboratory method Spraying nozzle Unexposed Pressure Air Soiling mix Spraying vessel Coupons of roofing products Soiled Spraying the soiling mix (5 30 sec) Drying w/ir lamp (1 2 min) Measurement of R ( 5-10 min) 19

20 Contribution of each surrogate to the reflectance spectrum dust unexposed; salts organics r (λ) soot Wavelength (nm) 20

21 Correlation of soot loading with R/R Reflectance Unexposed 0.12 μg/cm μg/cm2 0.4 μg/cm μg/cm μg/cm Wavelength (nm) R/R Deposited Black Carbon Soot (μg cm -2 ) 21

22 Sample conditioning and weathering QUV/Spray Weathering Tester (Qlab) 22

23 Effect of conditioning on initial solar reflectance Modified bitumen (n=1) 24h 72h Asphalt shingle (n=2) Single ply membrane (n=2) Tile (n=4) Metal/Factory applied coating (n=4) Field applied coating (n=6) Mean gain in initial solar reflectance Little change from conditioning alone 23

24 Effect of conditioning on soiling Field applied coating (n=6) Single ply membrane (n=2) Modified bitumen (n=1) Tile (n=4) Metal/Factory applied coating (n=4) Asphalt shingle (n=2) Soiling Weathering + Soiling Conditioning + soiling Absolute loss of solar reflectance Conditioning + Soiling Soiling 24

25 Effect of weathering on solar reflectance losses Field applied coating (n=6) Single ply membrane (n=2) Metal/Factory applied coating (n=4) Modified bitumen (n=1) Tile (n=4) Asphalt shingle (n=2) Weathering Conditioning + +Soiling Weathering Conditioning + Soiling + +Weathering Absolute loss of solar reflectance Conditioning + Soiling + Weathering Conditioning + Soiling 25

26 Effect of conditioning & weathering duration: 1 week y = x R² = SR (CSW -7 days of C&W) No change line: y = x No additional effect by prolonging conditioning nor weathering SR (CSW -1 day of C & W) 26

27 Specific surface characteristics (chemistry, rugosity) determine soiling retention Solar reflectance after lab exposure (C+S+W) Coating 1 Coating 2 Coating 3 Coating 4 Coating 5 Coating Initial solar reflectance n = 6 different coatings 27

28 Accelerated aging standard protocol Conditioning (QUV ASTM G 154) 24h total duration (2 cycles) 8 h of UV (0.89 mw cm -2 ), temperature: 60 C 8 h of water condensation: temperature: 50 C Soiling (Spraying ) Spraying of a mix of soot, humic acid dust and salts Total mass of soiling deposited is g Evaporate water by heating with IR lamp Weathering (QUV ASTM G 154) 1 week total duration (14 cycles) 8 h of UV (0.89 mw cm- 2 ), temperature: 60 C 8 h of water condensation: temperature: 50 C 28

29 Our method reproduces CRRC s 3-year-aged solar reflectance ratings in 3 days Solar Reflectance Field-Applied Coating Field applied coating (n=7) Metal or factory-applied coating (n=8) Accelerated aging (LBNL) Factory-Applied Coating Single-Ply Membrane Modified Bitumen Shingle Tile Metal y = (1.02 ± 0.03) x - (0.01 ± 0.02) R 2 =0.96 Single-ply membrane (n=11) Asphalt shingle (n=4) Clay tile (n=2) Modified bitumen (n=3) Three years of natural exposure (CRRC) 29

30 Discussion and development of accelerated soiling standards June 2012 & Dec 2012 Draft standard presented at ASTM Created Task Group D (Test Method for Accelerated Aging of Solar Reflectance of Roofing Materials) International Workshop on Advances in Cool Roof Research Berkeley, July 28-29, September 2012 Draft standard presented at ISO TC-163: Thermal performance and energy use in the built environment 30

31 Perspectives and items for discussion simple & reliable tunable method that mimics in just 3 days: CRRC 3-year average of three sites; AZ exposure; OH exposure not intended to test resistance to microbial growth or long-term mechanical durability Validation by inter-laboratory tests underway Integration in laboratory weathering hardware underway Future work: 1) Florida exposure: can it be predicted with this method? 2) Anti-soiling properties: can be predicted with this method? 3) further refinements (e.g., defining standard reference surfaces) 31

32 Acknowledgements U.S. Department of Energy (DOE/EERE/BTO) Our industrial partners CRRC: Sherry Haoand Jessica Clark ORNL: André Desjarlais LBNLteam: Chelsea Preble, Sharon Chen, Olivier Rosseler, Amandine Montalbano, Sarah Quelen, Lea Marlot, Mike Spears, Vasileia Zormpa, Tosh Hotchi, David Francois. 32